A. Field of the Invention
The present invention relates to lighting fixtures that produce high intensity, controlled, and concentrated light beams for use at relatively distant targets. One primary example is illumination of a sports field.
B. Problems in the Art
One type of wide area lighting fixture utilizes a lamp that includes an arc tube inside a glass envelope. One end of the lamp has an externally threaded metal base that is adapted to screw into a socket in the fixture. In this manner the lamps can be easily exchanged.
The lamps must be screwed in far enough so that appropriate electrical contact is made. Because of inherent manufacturing tolerances and other reasons, it is difficult to ensure that all lamps will end up in the same rotational orientation (position in a plane perpendicular the longitudinal axis of the lamp) when screwed into the socket.
This may not matter. However, certain lamps are designed to work best or are preferred in a certain rotational position. There is a need for way to ensure correct rotational position will occur for a lamp in a thread-in socket for these types of fixtures.
One example of a lamp that would benefit is the Z-lamp™ available from Musco Corporation, Oskaloosa, Iowa. It is disclosed at U.S. Pat. No. 5,856,721. This patent discloses ways in which the lamp and/or socket can be configured to try to insure consistent rotational position of the lamp (in this case to consistently ensure the longitudinal axis of the arc tube inside the glass envelope, which is angularly offset or tilted from the longitudinal axis of the lamp) ends up in a certain plane relative to either the fixture or to the ground. As explained in the patent, this promotes a reduction in tilt factor which can result in loss of light output from some of these types of lamps.
While these types of arrangements help ensure a predetermined rotational orientation of the lamp relative to the socket, it does not account for the fact the socket may end up in different rotational positions when installed in the fixture. Therefore, despite use of the methods disclosed in the Musco patent (e.g. pin on threaded base of lamp in alignment with plane of longitudinal axis of arc tube and helical slot in base with terminal end that would provide correct rotational orientation between lamp and socket), if the socket is not mounted in the correct position, the lamp may end up in the wrong rotational position.